This invention relates to a safety controller and a system using such a safety controller. In particular, this invention relates to a safety controller of the kind suitable for a safety circuit for a machine equipment such as fabrication machines and industrial robots and a system using such a safety controller.
Japanese Patent Publication Tokkai 2003-14072, for example, disclosed a safety circuit using a relay unit containing a plurality of electromagnetic relays for securing labor safety at a production site, adapted to supply electric power to a machine equipment such as fabrication machines and industrial robots only when their safe condition is assured. Such a relay unit serves to monitor the condition of a safety circuit on the basis of an input signal from a safety switch such as an emergency stop switch or a safety area sensor such as a safety door switch and to shut off the power source of such a machine equipment dependably if an abnormal condition has occurred and not to restart the machine equipment unless the cause of the abnormal condition has been removed.
In a system using a relay unit containing such electromagnetic relays, a logic is formed by wiring because the safety circuit is formed by the relay sequence and if there are many fabrication machines or the like to be controlled, the number of wires increases, the system becomes complicated and it becomes difficult to design such a system.
When it becomes desirable to modify a portion of a system in response to the user's request, such as when it becomes desirable, say, on a production line having a plurality of fabrication machines distributed at different work areas, to control the starting and stopping of a fabrication machine at a certain work area in correlation with another fabrication machine at a neighboring work area, its logic must be changed by the wiring and hence this requires a long time and a large amount of manpower.